In a known mineral breaker of the type for reducing rock, coal, rubble or the like, a rotating drum has a plurality of blow bars, impact bars or teeth, which as the roller rotates at high speed, impact large lumps and particles of the mineral causing reduction in mineral particle size. In some cases, the blow bars throw the mineral against a breaker plate, spaced apart from the roller. Reduction of the mineral material occurs by impact with the blow bars, impellers or teeth and by impact with the breaker plate.
Referring to FIGS. 1 and 2 of the accompanying drawings, there is shown a prior art mineral crusher assembly comprising a roller 1 arranged to rotate under power about an axle 2, the roller comprising a plurality of impeller bars 3 extending radially outward of the roller, an outer casing 4 comprising first and second opposite upright sides, a front panel 6, a back panel 7 and a roof, the roof being lined with a plurality of breaker plates 8, 9, 10 against which the mineral is thrown, and a grid 11.
On entering an open mouth 12 of the crusher, the mineral encounters the rapidly rotating roller 1 and is reduced by impact with the roller, and particularly the impeller bars 3. The impeller bars throw lumps of the material against the breaker plates 8, 9, 10 and the mineral repeatedly bounces backwards and forwards between the roller and the breaker plates, being reduced on every impact.
On reaching the rear of the crusher, the mineral drops down under gravity, and under force imparted by the rotating roller, onto the grid 11. The reduced mineral drops out from underneath the crusher into a hopper, conveyor belt or the like.
The maximum size of particle to which the mineral is reduced is largely determined by the distance between the final breaker plate 10 and the roller. The position of the final breaker plate 10 with respect to the roller is adjustable.
The resulting reduced mineral has a range of particle sizes varying from various small particles eg. grains of sand, through aggregate of 10 mm, 20 mm average particle size, up to the maximum particle size, eg. 100 mm. The reduced mineral may be separated and graded into different sized particles as required on exiting the crusher.
Final reduction of the mineral occurs at the grid 11 in the prior art crusher of FIG. 2. The grid 11 comprises a plurality of substantially parallel bars spaced apart from each other. The position of the grid with respect to the roller may be adjustable, and the grid may be swung away from the roller, being swung from a hinge.
The grid 11 is shown schematically in FIG. 3 herewith.
Another prior art crusher, shown in FIG. 4 herewith, operates similarly as the crusher of FIG. 2, except that the final reduction occurs by the hinged grid section 30 completely underneath the roller, between the front and rear panels of the casing.
However, there are problems with the prior art crushers where a non reducible item, eg. a piece of steel bar, or a large block of wood, is entered into the mouth of the crusher. The over size object may become lodged between the breaker plate and the roller, causing damage to the breaker plate, or causing the roller to stop rotating, with possible damage to the drive mechanism to the roller as well as to the breaker.
Further, the grid 11 and the semi circular grid 30 each experience a high degree of wear, leading to increased maintenance and running costs of the crusher.
Mineral crushers are disclosed in patent abstracts of Japan, volume 017, number 496 (C-1108), 8.09.1993 and JP 05131155A (Kurimoto Limited), 28.05.1993 and volume 016, number 584 (C1013), 24.12.1992 and JP 04235753A (Kurimoto Limited), 24.02.1992. However, the crushers disclosed in these documents appear to incorporate relatively complicated adjustment apparatus in order to move a breaker plate and a collection member. Also the collection member appears to be rather small and particles resulting from crushing minerals entered into the crusher may not necessarily all accumulate within it.
In GB-A-633102 (Pattinson) a crushing machine which utilizes material which has already been crushed in an attempt to aid crushing of new material and prevent undue wear on the striking surfaces of the crushing machine is disclosed. However, the machine does not appear to have any provisions should an oversized piece of material be entered into it, thereby risking damage to the machine. In FR-A-2323444 (Hazemag) apparatus is disclosed having a breaker which may be adjustable. However, the crusher does not appear to be capable of varying the amount of ground mineral accumulated.